X-ray or gamma ray systems or devices – Specific application – Fluorescence
Reexamination Certificate
1999-04-26
2001-05-01
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Fluorescence
C378S044000
Reexamination Certificate
active
06226347
ABSTRACT:
This application claims Paris Convention priority of German patent application number 198 20 861.8 filed May 9, 1998, the complete disclosure of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The invention relates to a spectrometer for the simultaneous measurement of several spectral lines of a sample with several wavelength selectors each selectively supplying light of a certain wavelength to a detector, wherein usually each wavelength selector selects a different wavelength.
A multiple channel spectrometer of this type is e.g. supplied by the company Bruker AXS GmbH (see manual “Mehrkanal-Rö ntgenstpektrometer MRS 4000” dated 1997).
In order to examine the optical characteristics of samples, in particular for determining the chemical composition on the basis of specific, optical characteristics of the different atoms and molecules, a multitude of most different spectrometers is used which operate in wavelength ranges from the far-infrared via the visible range to the range of X-rays. In all these spectrometers the sample to be examined is irradiated with light of one or several wavelengths and the light modified by the sample, being characteristic of the sample, is detected either in transmission or reflection and is evaluated in the form of a spectrum.
To obtain spectral resolution of the detected measuring signals, up to now two alternative methods have been used, i.e. the use of an energy-dispersive or a wavelength-dispersive arrangement.
An energy-dispersive spectrometer usually comprises only one single detector which directly receives the radiation to be examined from the sample. Since the detector “faces the sample directly” it does not only receive the interesting “useful radiation” but also the entire background and interfering radiation. In particular, often the detector will be highly influenced by the radiation of the main elements which sometimes are of no interest whatsoever since they are known anyway. In this manner, the signals of the actually interesting elements disappear inside the strong background or interference signals. As a consequence, an energy-dispersive spectrometer of this type has only low resolution and a high detection limit and therefore a relatively low overall performance.
As an alternative, wavelength-dispersive spectrometers are used, like e.g. the initially cited multiple channel X-ray spectrometer “MRS 4000”. These devices comprise a multitude of analyzers and detectors, wherein each element to be measured has its own analyzer crystal and its own detector. In this manner, it is possible to receive the signals of various wavelengths simultaneously. The wavelength-dispersive spectrometers are thus very powerful and have a high resolution.
However, the big effort required owing to the many detectors and associated measuring electronics for each wavelength range and the increased vulnerability to disturbances due to the multitude of highly sensitive components is a disadvantage. In particular, the required large number of detectors and independent measuring electronics associated therewith render such spectrometers quite expensive.
WO 97/05474 on the other hand discloses a wavelength-dispersive X-ray fluorescence spectrometer which provides for several analyzers operating in different wavelength ranges with only one single detector. However, this spectrometer does not allow simultaneous measurements of light from all analyzers, but can receive the light from only one single analyzer at a time. By means of corresponding mechanics, the various monochromators consisting each of a focussing analyzer crystal with entrance and exit gap, are successively brought between the sample and the detector and thus the individual parts of the spectrum are recorded successively.
This arrangement has the disadvantage that on the one hand only one single spectral line can be measured at a time. Therefore the spectrometer works extremely slowly compared to other known wavelength-dispersive arrangements like e.g. the above-mentioned “MRS 4000”. Although the same detector is used for a variety of different wavelength ranges, its energy dispersion which is of course usually present is not utilized. Furthermore, owing to its moveable parts the device according to WO 97/05474 has the disadvantage of a high mechanical effort, and during operation the complicated mechanics will frequently lead to operational faults.
In contrast thereto, it is the object of the present invention to present a spectrometer for the simultaneous measurement of several spectral lines with the initially described features and which on the one hand achieves the high resolution of known wavelength-dispersive arrangements in combination with relatively short measuring times by simultaneous measurements of different wavelength ranges but which on the other hand considerably reduces the complexity of the apparatus, in particular the number of detectors and associated measuring electronics without having to increase the constructional effort with respect to the mechanical apparatus to a considerable extent.
SUMMARY OF THE INVENTION
According to the invention, this object is achieved in a manner which is at the same time surprisingly simple and effective, in that at least two different wavelength selectors can supply light from the sample to the same detector and that the detector is energy-dispersive and has a sufficiently large resolution in order to separate the energies of the detected light quanta of different wavelengths coming from the at least two different wavelength selectors.
The inventive spectrometer selects at first only the characteristic radiation of the elements to be analyzed from the total radiation emitted by the sample via individual wavelength selectors, just like a conventional wavelength-dispersive spectrometer. Subsequently however, several characteristic lines are simultaneously processed by one single detector in an energy-dispersive manner, whereby the number of detectors can be reduced by at least a factor of 2, in certain embodiments by an even higher factor, in comparison to a conventional wavelength-dispersive spectrometer working simultaneously. In contrast to a purely energy-dispersive spectrometer, in the inventive spectrometer hardly any background radiation reaches the detector and the detector is not overloaded by a main component of the radiation from the sample, which considerably improves the numerical statistics for the remaining interesting elements. In principle, the invention combines the positive characteristics of a wavelength-dispersive simultaneous spectrometer by combining several wavelength-dispersively separated lines on one single detector with the advantages of a conventional energy-dispersive arrangement without having to accept their disadvantages.
In a particularly preferred embodiment, the inventive spectrometer is an X-ray fluorescence spectrometer, wherein the light detected by the sample is X-ray fluorescence light. The spectrometer according to the present invention was developed especially for this application. However, the above-mentioned basic idea of combining the positive characteristics of an energy-dispersive spectrometer and a wavelength-dispersive arrangement can be transferred also to other wavelength ranges.
In case relatively inexpensive detectors with limited energy resolution are used, it is advantageous to provide several detectors each receiving light from the sample only via a few, in the most simple case via only two different wavelength selectors. Even with a relatively low energy resolution of the detector, it will always be possible to select two suitable characteristic lines (or narrow wavelength ranges) out of the interesting ones, which have are sufficiently separated from one another to permit safe separation even using a detector with low energy resolution.
In an extreme case, all interesting characteristic lines can be processed by only one single detector with correspondingly high resolution. In this case the detector should have an energy resolution of &Dgr;E<200 eV, preferably &
Bruker AXS Analytical X-Ray Systems GmbH
Kiknadze Irakli
Kim Robert H.
Vincent Paul
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